Reach all the way. No matter what the game is ALWAYS encouraging you to play and I don’t like it as much as 3 but I will keep going back until I want to play a different Halo game.
Halo 4 had an under rated progression system, my only problem with it was that it was too short/easy to get through. But between these two I like Reach, though it has the opposite problem 4 had for me.
It was actually one of the best systems of it’s time, you had to be there to understand. Ranks were acquired after reaching a certain amount of xp and the required xp wasnt as high as you think.